Pearlescent additives, also known as pearlizing agents, are added to beauty and personal care products such as hair and skin care products to provide a pearly appearance to the products. Chemicals which are tiny (micron size) needles or platelets often exhibit this pearly appearance. Materials which exhibit this effect are ethylene glycol mono-and di-stearate, TiO.sub.2 coated mica, bismuth oxychloride, and natural mother of pearl. Many organic materials exhibit this pearlescence provided they can be produced in an appropriate needle or platelet shape. Ethylene glycol distearate (EGDS) or ethylene glycol monostearate (EGMS) are the most commonly utilized pearlizing agents.
Obtaining good pearlescence requires obtaining the appropriate crystallization. Consistency in obtaining the appropriate size and type of crystal formed is difficult especially when utilizing ethylene glycol distearate or the like. The controlled formation of EGDS crystals of the proper size to give good pearlescence depends on two major steps of the crystallization process. The first step is the solubilization by addition of EGDS to the hot (above EGDS's melting point) beauty or personal care product, for example a shampoo. Good, efficient solubilization of the EGDS depends on being above the melting point, finely emulsifying the melted EGDS, and allowing enough mixing time for the solubilization to occur. As the shampoo composition, for example, is varied, it is generally necessary to insure that it can solubilize the EGDS at a temperature greater than EGDS's melting point but then also precipitate it at a temperature less than the melting point. If a composition has too high a solubilizing capacity the EGDS may not crystallize out, may require too low of an outlet temperature (&lt;100.degree. F.) to crystallize or may only crystallize slowly leading to crystals that are too large. If the solubilizing capacity is too low, only part of the EGDS will be solubilized and upon cooling the unsolubilized EGDS will freeze out as large chunks.
In the second step, the precipitation or freezeout step, composition and the cooling process are important parameters. The composition should not have too high a solubilization ability as discussed. Several cooling processes are known in the art. Some methods nucleate crystals in only a portion of the composition and then mix these seed crystals back into the warmer composition. A single-pass method is better for controlling crystal size since it does not require remixing crystals into the uncooled composition. Many factors, such as flow rate, temperature and time, must be monitored and controlled to achieve appropriate crystal size. The formation of crystals depends very much on the rate of cooling. An imperfect cooling will decrease the pearlescence and the heating and cooling may have to be repeated until a satisfactory pearlescence is achieved.
Obviously, achieving consistency in the crystallization process requires constant monitoring as well as attending to adjustments. The difficulty in controlling the process translates to an inconsistency in the pearlescence of the compositions and expenditures in time and money.
A pearlizing concentrate which can be added to beauty and personal care compositions without a need for crystallization, with its requisite heating and cooling elements, can provide significant benefits. It can be added at room temperature saving energy and equipment costs and offer a more consistent pearlescence since many of the sensitive parameters of a crystallization process have been removed.